[Coin-discuss] bestPossibleObjective for Cbc

[Kish Shen]

John,

Thanks. I have just downloaded Coin-Cbc in branches/devel, and the 
bestPossible is indeed working.

I still get a failure instead of unbounded state returned for a simple 
unbounded problem. I need more time to look at the code to see what has 
changed.

I am however having problems with maximising problem -- I was doing my 
unbounded test case with a maximising problem:

max X

X = Y
X + Y >= 3
X is integer

but this problem is now returning X, Y = 2, i.e. it seems to be minimising the 
problem rather than maximising! 

I have not had time to look at this in detail, but thought I should post this 
before I leave today.

Cheers,

Kish
On Tuesday 11 July 2006 23:12, John J Forrest wrote:
> Kish,
>
> bestPossible should be fixed in branches/devel - also unbounded.
>
> John Forrest
>
>
>
>              Kish Shen
>              <kish.shen at crossc
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>                                        [Coin-discuss]
>                                        bestPossibleObjective for Cbc
>              07/10/06 10:24 PM
>
>
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>
> Hi,
>
> I am interested in obtaining the best possible bound on the objective value
>
> from a MIP solve. This value is stored in bestPossibleObjective in the
> CbcModel, but it seems that if the MIP search is exited without searching
> the
> whole tree, because of setting of the allowable MIP gap (e,g, as specified
> by
> CbcAllowableFractionGap), bestPossibleObjective is set to bestObjective at
> the end of the search.
>
> For example, in the following MIP solve of the bell3a problem:
>
> Cbc0012I Integer solution of 878430 found by heuristic after 150 iterations
>
> and 2 nodes (1.46 seconds)
> Cbc0010I After 500 nodes, 156 on tree, 878430 best solution, best possible
> 876741 (8.18 seconds)
> Cbc0011I Exiting as integer gap of 1689.38 less than 1e-10 or 0.3%
> Cbc0001I Search completed - best objective 878430, took 5109 iterations and
>
> 501 nodes (8.19 seconds)
>
> the search is exited early, with
>
> bestPossibleObjective = 876741
> bestObjective = 878430
>
> but by the time I call getBestPossibleObjValue() immediately after the
> branchAndBound() call, it is already set to 878430. [I think this is done
> around line 1700 of my copy of CbcModel.cpp]
>
> Is there any way I can get the original bestPossibleObjective before it was
>
> set to bestObjective?
>
> Thanks and cheers,
>
> Kish
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